(1) Technical Field of the Invention
The present invention provides a process for producing the ceramic porous body comprising the steps of (1) forming micelles in liquid by mixing {circle around (1)} surfactant molecules, {circle around (2)} surfactant molecules and given organic molecules, or {circle around (3)} different kinds of surfactant molecules, (2) forming a precursor of a ceramic porous body having an organic-inorganic structure is formed through mixing a ceramic material or a precursor of the ceramic material into the liquid containing the micelles, the precursor of the ceramic porous body comprising a template having the micelles arranged in a hexagonal, cubic or lamella form and the ceramic material or the ceramic material precursor adsorbed around the micelles, (3) removing the surfactant molecules or the surfactant molecules and the given organic molecules in the precursor of the ceramic porous body by photo-oxidation through irradiating vacuum ultraviolet light upon the precursor to leave an inorganic skeleton alone, and (4) thereby forming the ceramic porous body having nanometer-scale pores at a low temperature.
(2) Related Art Statement
The ceramic porous bodies are expected to be used in various fields including absorption and separation. According to the IUPAC""s classification, the porous bodies are classified into microporous solids having pore diameters of 2 nm or less, mesoporous solids having pore diameters of 2 to 50 nm and macroporous bodies having pore diameters of 50 nm or more. If the pore diameters can be arbitrarily and finely controlled, the ceramic porous bodies can be expected to be selectively applied as adsorption materials, catalyst materials, high separation materials, etc.
As a process for producing a mesoporous or macroporous material, it is proposed that micelles of surfactant molecules and given organic molecules coexisting therewith, or micelles of different kinds of surfactant molecules are used as a template, a precursor of the ceramic porous body having an organic-inorganic structure is formed by mixing the micelle template with a ceramic material or a precursor of the ceramic material, and then surfactant molecules or the given organic molecules in the precursor are removed by heating or treatment with an acid. This method is generally called xe2x80x9cSupermolecular template methodxe2x80x9d. For example, see Makoto Ogawa, xe2x80x9cSupermolecular template methodxe2x80x9d, Coloring materials, 71 (10), pp 646-655, 1998. However, removal of the given organic molecules or the surfactant molecules under heating may cause stress inside the material, which results in troubles such as cracking or peeling. Further, it has been difficult to coat or form a ceramic porous body on a surface of a material having low heat resistance, for example, a plastic material.
In view of these circumstances, the present inventors have made strenuous researches, and discovered that (1) micelles are formed in liquid by mixing {circle around (1)} surfactant molecules, {circle around (2)} surfactant molecules and given organic molecules, or {circle around (3)} different kinds of surfactant molecules, (2) a precursor of a ceramic porous body having an organic-inorganic structure is formed through mixing a ceramic material or a precursor of the ceramic material into the liquid containing the micelles, the precursor of the ceramic porous body comprising a template having the micelles arranged in a hexagonal, cubic or lamella form and (3) the surfactant molecules (which may include the given organic molecules) in the precursor of the ceramic porous body are removed by photo-oxidation through irradiating vacuum ultraviolet light upon the precursor to leave an inorganic skeleton alone, and (4) thereby the ceramic porous body having nanometer-scale pores is formed at a low temperature.
As to the surfactant, it is known that it takes various molecular assemblies (liquid crystal-like structures) such as hexagonal, cubic or lamella structures. If the surfactant exceeds its critical micelle concentration, the surfactant molecules first form spherical micelles, and then form rod-shaped micelles through association when the surfactant concentration further increases (See FIG. 1(a)). As the surfactant concentration further increases, the rod-shaped micelles are arrayed at an interval of a few or several nm, for example, thereby forming hexagonal-, cubic- or lamella-structure rheotropic liquid crystals. See FIG. 1(b). Although in FIG. 1(b), only six rod-shaped micelles surround the central one, many rod-shaped micelles surround the central one as in FIG. 1(b). The thus formed micelles uniformly arrayed are used as templates. As to the mesopore structure, it may be formed as follows: First, a ceramic material or the like occupies the spaces among templates and subsequently, organic-inorganic mesostructures would be formed by a chemical interaction. The above is known from xe2x80x9cPorous Materialsxe2x80x94Characterization, Production and Applicationxe2x80x94xe2x80x9d, edited by Y. Takeuchi, Published by FUJI TECHNOSYSTEM CO., LTD. pp 101 to 104, and C. T. Kresage, M. E. Leonowicz, W. J. Roth, J. C. Vartul; and J. S. Beck, Nature 359 (1992) 710-712. Finally, the calcination process eliminates the organic species in such mesostructures, having ceramic material or the like with mesopore structure.
The present inventors have made strenuous researches, and discovered that {circle around (1)} micelles of surfactant molecules, {circle around (2)} micelle of surfactant molecules and given organic molecules coexisting therewith or {circle around (3)} micelles of different kinds of surfactant molecules are used as a template, a precursor of the ceramic porous body having an organic-inorganic structure is formed by mixing the micelle template with a ceramic material or a precursor of the ceramic material (FIG. 1(c), the surfactant molecules (which may include the given organic molecules) in the precursor of the ceramic porous body are removed by photo-oxidation through irradiating vacuum ultraviolet light upon the precursor to leave an inorganic skeleton alone, and thereby the ceramic porous body having nanometer-scale pores is formed at a low temperature (FIG. 1(d)). The present invention has been accomplished based on this discovery.
That is, the present invention provides a low temperature producing process, which particularly effectively produces the ceramic porous body comprising an inorganic skeleton and having nanometer-scale pores by removing the surfactant molecules (which may include the given organic molecules) in the form of a template as carbon monoxide, carbon dioxide and water by photo-oxidation through irradiation of vacuum ultraviolet light upon it.
In order to solve the above problems, the present invention provide the following countermeasures.
(I) The present invention provides a process for producing the ceramic porous body comprising the steps of (1) forming micelles in liquid by mixing {circle around (1)} surfactant molecules, {circle around (2)} surfactant molecules and given organic molecules, or {circle around (3)} different kinds of surfactant molecules, (2) forming a precursor of a ceramic porous body having an organic-inorganic structure is formed through mixing a ceramic material or a precursor of the ceramic material into the liquid containing the micelles, the precursor of the ceramic porous body comprising a template having the micelles arranged in a hexagonal, cubic or lamella form and the ceramic material or the ceramic material precursor adsorbed around the micelles, (3) removing the surfactant molecules or the surfactant molecules and the given organic molecules in the precursor of the ceramic porous body by photo-oxidation through irradiating vacuum ultraviolet light upon the precursor to leave an inorganic skeleton alone, and (4) thereby forming the ceramic porous body having nanometer-scale pores at a low temperature.
(II) The present invention further provides a process for producing the ceramic porous body comprising the steps of (1) forming micelles in liquid by mixing {circle around (1)} surfactant molecules, {circle around (2)} surfactant molecules and given organic molecules, or {circle around (3)} different kinds of surfactant molecules, (2) forming a template comprising the micelles arranged in a hexagonal, cubic or lamella form, (3) forming a precursor of a ceramic porous body having an organic-inorganic structure through mixing a ceramic material or a precursor of the ceramic material into the liquid containing the micelles, the precursor of the ceramic porous body comprising the template and the ceramic material or the ceramic material precursor adsorbed around the micelles, and (4) removing the surfactant molecules or the surfactant molecules and the given organic molecules in the precursor of the ceramic porous body by photo-oxidation through irradiating vacuum ultraviolet light upon the precursor to leave an inorganic skeleton alone, and (5) thereby forming the ceramic porous body is having nanometer-scale pores at a low temperature.
(III) The present invention further provides a process for producing the ceramic porous body comprising the steps of (1) forming micelles in a liquid by mixing {circle around (1)} surfactant molecules, {circle around (2)} surfactant molecules and given organic molecules, or {circle around (3)} different kinds of surfactant molecules thereinto, (2) forming a precursor of a ceramic porous body having an organic-inorganic structure by mixing a ceramic material or a precursor of the ceramic material into the liquid containing the micelles, the precursor of the ceramic porous body comprises a template having the micelles arranged in a hexagonal, cubic or lamella form and the ceramic material or the ceramic material precursor adsorbed around the micelles, (3) removing the surfactant molecules or the surfactant molecules and the given organic molecules in the precursor of the ceramic porous body by photo-oxidation through irradiating vacuum ultraviolet light upon the precursor to leave an inorganic skeleton alone, and (4) thereby forming the ceramic porous body having nanometer-scale pores at a low temperature. In FIGS., 2(a) and 2(b), a cubic form and a lamella form of the micelles are shown.
The following are preferred embodiments of the process for producing the ceramic porous body according to the present invention.
(1) The ceramic material or its precursor for ceramic porous body having the organic-inorganic structure is selected from materials which allow vacuum ultraviolet light to pass through them.
(2) The ceramic material or its precursor for the precursor of the ceramic porous body having the organic-inorganic structure is selected from materials which absorb vacuum ultraviolet light and emit electrons through their optically catalytic action.
(3) The surfactant molecules in the precursor of the ceramic porous body having the organic-inorganic structure are removed by irradiating vacuum ultraviolet light upon it.
(4) The surfactant molecules in the precursor of the ceramic porous body having the organic-inorganic structure are removed by irradiating vacuum ultraviolet light upon it in an atmosphere at 200xc2x0 C. or less. If the temperature is 300xc2x0 C. or more, the surfactant molecules are thermally decomposed, which disturbs the finely porous structure. Therefore, 200xc2x0 C. or less is employed, considering the safety.
(5) The precursor of the ceramic porous body having the organic-inorganic structure is shaped in a thin filmy form.
(6) The precursor of the ceramic porous body having the organic-inorganic structure is shaped in a finely particulate form.